In the formation of integrated circuits on the surface of a semiconductor substrate, oxide or oxynitride layers are frequently grown or deposited over the surface of a crystalline substrate such as silicon. Oxide or oxynitride layers may have superior electrical properties, including high electron mobility and low electron trap densities, that are desirable for device operation in semiconductor applications. Several methods have been developed for forming oxide and oxynitride layers for semiconductor applications and, following formation of these layers on a substrate, oxide and oxynitride layers are frequently annealed in to further improve their material and electrical properties.
In one example, a thin oxide layer may be annealed in the presence of a nitrogen-containing gas, such as nitrous oxide (N2O), at predetermined processing conditions to form an oxynitride layer by nitrogen incorporation from the gas into the oxide layer. In another example, an oxynitride layer may be formed on a substrate by annealing a clean substrate in the presence of a N2O gas. However, one serious shortcoming associated with using a N2O gas for oxide annealing and nitrogen incorporation is tool-to-tool variability among similar or dissimilar processing tools and processing tool configurations. Tool-to-tool variability can result in unacceptable thickness variations and different nitrogen depth profiles in the oxynitride layers. In other words, processing tool A may have different process results as compared to processing tool B, even if the same N2O oxidation process recipe and hardware configuration are used.
Potential solutions to these shortcomings associated with N2O annealing include tighter control on hardware design and manufacturing, in particular with respect to quartz system components commonly used in batch processing tools. However, this is an expensive and impractical option because quartz system components are often manufactured by hand.
There is thus a need for new methods that reduce or eliminate these and other shortcomings and disadvantages associated with N2O-based oxidation processes.